I was driven out of a decent neighborhood when a slumlord bought a unit in my complex. The main problem was relentless bass and their belief that they were entitled to listen to it whenever they felt like it, at home, in cars pulling up, etc. They were willfully ignorant of how subwoofers propagate even "low level" bass. It lead to several police calls, which didn't go well (the cops tried to be politically-correct and the real issue got diluted). This was about 8 years ago and the growth of wireless speakers (Bluetooth racket in any location) has only made it worse. Headphones compensate sometimes, but they ought to be mandatory in all shared-wall situations.

These people claim to be reasonable but the minute you mention a noise problem, they take their usual victim/culture stance and it's rare that the situation gets better. You (as the complainer) become identified with "oppressive" authority figures and the original reason for the complaint gets lost in the ensuing politics.